In life, Kalenax was an unholy terror. Even though he was not very old, this red dragon carved a path of destruction and violence across huge areas. His lust for violence and riches drew the attention of Tiamat, who blessed him with even more power. The devestation was incredible, but eventually even such a powerful creature might fall. And so Kalenax did, hunted and killed by a group of adventurers who died to the last in their effort to bring the dragon down.
But even in death, Kalenax was not finished with his rampage. Tiamat-worshipping kobolds of the Poison Scale tribe eventually found the broken and skeletal remains of Kalenax years later and immediately recognised, though signs and portents, that Kalenax had been divinely blessed by their own patron. Not ones to pass up a bounty, the kobolds broke down teh skeleton and fashioned tribal relics from the bones. Kalenax's skull was fashioned into a shield, banded with iron and blessed twice-over by Tiamat, for the chieftan to use.
The kobolds themselves ran afoul of adventurers later and so the Skullshield of Kalenax came to be in the world at large, where many fought over it. Consecrated with unholy power and still containing the whispering remnants of Kalenax's spirt, the shield is an artifact of incredible power. The ablility to blast white hot flames that can melt metal or stone and protect the user from the same is powerful enough, but the shield also grants the wearer the power to sense nearby magical items and perform certain rituals like a master. Dragonkin of all kind are instinctively unsettled before the sight of the shield, though followers of Bahamut may instead be enraged at being near a relic of their hated foe.